Prevention of methacrylate and acrylate ester polymerization in production thereof



v United States Patent PREVENTION OF METHACRYLATE AND ACRY- LATE ESTER POLYMEREZATEGN IN PRODUC- TION THEREOF Hugh J. Hagemeyer, Jr., Alden E. Blood, and Max Statman, Longview, Tern, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Dec. 10, 1964, Ser. No. 417,504

8 Claims. (Cl. 260-486) This invention relates to an improved method for the production of monomeric methacrylate and acrylate esters.

This application is a continuation-in-part of our copending application Ser. No. 124,799, filed July 18, 1961, now abandoned.

It is known that acrylic amides can be converted to esters by reaction at elevated temperatures with an appropriate alcohol in the presence of water and a strong acid, preferably a mineral acid such as sulfuric acid. Methacrylamide reacts under these conditions, for example, with methyl alcohol, butyl alcohol, etc. to give the corresponding alkyl methacrylates. However, it has been found that esters of this kind polymerize so readily that process equipment becomes plugged with polymeric material and keeps the yield of monomers at relatively low levels. To overcome this disadvantage, it has been proposed to employ well known polymerization inhibitors such as hydroquinone, diphenylamine, phenol, pyrogallol, tannic acid, copper, sulphur and other compounds of similar nature. Air and oxygen have also been proposed as inhibitors. While these compounds decrease the amount of polymer formed, they do not completely eliminate it, especially in processes employing packaged reactors and packed distillation columns where the conditions are such as to prevent the use of organic inhibitors and, therefore, require inorganic inhibitors which are less effective than organic inhibitors.

We have now found that polymerization of methacrylate and acrylate esters in the preparation of the monomeric ester compounds in proces equipment such as packed distillation columns and packed reactors is prevented by using ceramic packing therein which has been treated with a strong mineral acid and more especially a nitric-sulfuric acid mixture. The effective life of the thus treated packing is so great that no decrease in activity, i.e. prevention of polymerization, was found after two months of continuous operation of such process and equipment.

It is, accordingly, an object of the invention to provide an improved process for the preparation of monomeric methacrylate and acrylate esters. Another object is to prevent polymerization of said esters in the process and purification of the same. Another object is to provide a novel acid treated packing material that prevents polymerization of the said monomers during processing of the same. Other objects will become apparent hereinafter.

In accordance with the invention, we prevent the polymerization of monomeric methacrylate and acrylate esters in the preparation and purification thereof by packing the distillation column of the reactor with ceramic materials ordinarily used as a packing but which have been first treated with a mixture of strong mineral acids or other compounds that produce oxides of nitrogen under the conditions leading to bonding or absorption of the oxides of nitrogen or their ions or radicals to the ceramic packing. It is of particular significance that the ostensibly equiv- 3,33Zfi84 Patented July 25, 1967 "ice alent procedure of introducing oxides of nitrogen into the column or the reactant feeds rather than to treat the packing material is in fact quite ineffective in preventing polymerization in the reactor as illustrated by the following experiment:

A glass column 48 inches long and 1.61 inches in diameter'containing cubic inches of A inch unglazed porcelain Berl saddles was heated with a Chromel wire-Wound jacket. The lower end of the column was maintained at about 105-115" C. and the upper end at about 101-1l0 C. A 2'-liter reboiler (base heater) containing a water solution of ammonium acid sulfate and sulfuric acid maintained at about 112l24 C. was connected to the bottom of the column. Methacrylamide prepared by the amide synthesis from 2,810 ml. of acetone cyanohydrin and 3,660 ml. of percent sulfuric acid was fed at a substantially constant rate during the course of 17.3 hours into the top of the column maintained at about 98105 C. along with 8,200 ml. of water. 10,225 ml. of isobutanol was vaporized at 108 C. and fed to the reboiler at a substantially constant rate also during the course of said 17.3 hours and was carried up the column with steam fed into the reboiler via a water vaporizer. As the amide acid solution flowed down the reactor it reacted with the alcohol vapor and produced the methacrylate ester. The ester was vaporized and carried out of the column into a decanter along with unreacted alcohol and water. The coproduct ammonium acid sulfate flowed down the column to the reboiler Where it was removed through a drain. Substantial amounts of nitric oxide was added to the methacrylamide-feed solution and also to the reboiler in carrying out the above process. Suflicient nitric oxide was added to the methacrylamide-feed solution to saturate the same with nitric oxide, and nitric oxide was fed to the reboiler at approximately 20 ml. (S.T.P.) per minute. Air was also introduced into the reboiler at 50 to 100 ml. per minute in an attempt to further inhibit polymerization. At the end of said 17.3 hours of operation, the reactor became completely plugged with polymer and was thus rendered totally ineffective.

The treatment of the ceramic packing is carried out conveniently by soaking the packing in a nitric-sulfuric acid mixture for several hours, removing the acid mixture, and then washing the so-treated packing with water. The acid concentrations for both the nitric acid and the sulfuric acid may be varied from the strength of commercial concentrated acids to fuming acids containing varying amounts of the free anhydrides, for example, concentrated nitric acid containing free N0 and concentrated sulfuric acid (oleum) containing free S0 In the case of the latter, the S0 content may be for technical grades up to 66%, while a content as high as 90% is known. The ratio of nitric to sulfuric acids is not critical as long as appreciable amounts of both acids are present in the acid mixture. Actually any mixture of acids or other compounds that produce oxides of nitrogen can be used; for example, a mixture of concentrated sulfuric acid and various salts of nitric and nitrous acids such as nitrates or nitrites. The preferred acid mixtures for treating the packings employed in the invention comprise combinations of concentrated sulfuric acid or oleum and concentrated nitric acid. A typical mixture comprises equal volumes of the concentrated acids. Another efficacious mixture comprises equal volumes of concentrated nitric acid and oleum containing 20 percent of S0 The temperature of the mixtures as used for treating the packing also is not critical, but generally in the range of about 60 C., and preferably at or about normal room temperatures of 30 C. The time of treatment should be sufficient to activate the packing, but advantageous results are obtained with treatment periods as low as 15 minutes and up to 12-24 hours; however, no additional advantage appears obtainable by prolonged treatments.

Suitable ceramic packing that can be treated according to the invention includes any ceramic materials used as packing for one reason or another in chemical reactors and columns. By the term ceramic as used in the invention is meant to apply to porcelain and stoneware products prepared from varying amounts of clay, flint and feldspar. Porcelain and stoneware differ primarily in porosity. Chemically speaking, ceramic materials are composed of aluminum silicate, silica and potassium aluminum silicate so that any material containing these or analogous components would be operable in the invention whether called :eramics, porcelain, stoneware, etc., or not. Thus, packngs now known which can be used eflicaciously in the aractice of our invention include ceramic or ceramic-like shaped articles known in the art under the names of Raschig rings, Lessing rings, Cross-partition rings, Spiral rings, Intalox rings, but more particularly Berl saddles which is the preferred packing. Actually, the packing to )e treated can be in any shaped form desired, the object Jeing to bring the treated and activated ceramic or ceramc-like material in intimate contact with the monomer iquid and/or vapor. This can be carried out in any conlentional equipment that utilizes a packing in the processng of methacrylate and acrylate esters. Advantageously, he equipment comprises a tubular reactor and fractionatng column packed with the mentioned ceramic packing naterials which have been treated in accordance with the nvention, and provided with conventional heating, feedng withdrawal and refluxing means, but preferably havng the amide feed enter the upper region of the column ind the alcohol feed enter the lower region of the col- 111111, the formed esters passing overhead to a condenser vhile sulfuric acid or other such strong acid, water and ummonium salts are removed from the base through a [rain connected at the base of the column.

In carrying out the process of the invention, the reictants comprising methacrylamide or acrylamide, alco- 101, a strong acid selected from the group consisting of 50 HCl and H PO with sulfuric acid being preerred, and water, are passed into the reactor column conaining the acid treated ceramic packing material. The lseful strong acids may generally be defined as those vhich ionize in water essentially 100% to give hydronium ans and the acid anion. The amide feed containing the trong acid is preferably passed in liquid form into the olumn at or near the top of the column, and the alcool feed and Water feed is passed into the column at or ear the base of the column, while the strong acid, water nd ammonium salts are removed from the base through suitable drain. The water is preferably added to the ase reboiler in the form of steam. Advantageously, pheolic inhibitors such as phenol, cresol, etc., and air are lso added to the column, the former at the top section nd the latter at the bottom section to inhibit polymerizam in the reboiler section of the reactor column. Howver, these types of inhibitors are wholly ineffective by iemselves in preventing polymerization of the unsaturted monomers in the esterification and fractionating secons of the column. While the invention is applicable to atch processes, it is primarily adapted to a continuous rode of operation wherein the addition and withdrawal f materials are carried out continuously and so regulated s to balance one another. The column need be shut down nly at intervals of several weeks or more to replace with reshly mixed acid treated packing, whereas in similar oprations employing untreated packing, severe clogging of 1e column from polymer formation therein occurs in bout a day or less of operation.

The following examples will serve to illustrate further the manner of carrying out the process of the invention.

Example 1 This example is for comparison purposes and illustrates the very much improved results obtained by the process of the invention employing a ceramic packing material pretreated with a mixture of nitric and sulfuric acids in the reactor column as compared with the results obtained with the untreated ceramic material under the same conditions of reaction.

The reactor employed in the following Experiments A and B consisted of a glass column 48" long and 1.61" in diameter containing cubic inches of A unglazed porcelain Berl saddles. The reactor was heated with a Chromel wire-Wound jacket. Isobutanol was fed into the 2- liter base heater with a Cerveny micro-bellow pump. Air was introduced into the base at rates of 50100 ml. per minute as a polymerization inhibitor. Aqueous methacrylamide containing sulfuric acid was fed to the top of the reactor while a preheater was used on the alcohol feed to the base. A decantor separated water from the crude product. Sulfuric acid, water, and ammonium salts were removed from the base through the drain. In Experiments C and D, the reactor was increased in size to 72" x 2.0" and contained 220 cubic inches of A unglazed porcelain Berl saddles.

(A) Aqueous methacrylamide prepared in the amide synthesis from 2,810 ml. of acetone cyanohydrin and 3,660 ml. of percent sulfuric acid was fed into the top of the reactor with 8,200 ml. of water while 10,225 ml. of isobutanol was fed to the base heater all during the course of 15.8 hours. Phenol and air were also fed into the reactor during this time to inhibit polymerization in the reboiler section of the reactor. A total of 5,124 g. of crude organic product was obtained from the decantor when the reactor column became plugged with polymer. This is equivalent to 56.8 grams of organic product per cubic inch of Berl saddles.

(B) The reactor packing was then replaced with A" unglazed porcelain Berl saddles which had been treated as follows:

Clean Berl saddles were covered with a mixture prepared fro-m equal volumes of fuming sulfuric acid (20 percent sulfur trioxide) and concentrated nitric acid. After 12 hours, the acid mixture was poured off and the saddles were washed twice with water.

The reactor was run as before feeding methacrylamide obtained from the reaction of 32,770 ml. of acetone cyanohydrin and 37,160 ml. of 100 percent sulfuric acid along with 34,980 ml. of water and 90,000 ml. of isobutanol during the course of 162.1 hours. Phenol and air were added as in above A. During this time, there was obtained 88,134 g. of crude isobutyl methacrylate from the decantor. This is equivalent to about 980 grams of product per cubic inch of Berl saddles. The reactor was shut down for modification. Examination of the packing showed no sign of any polymer.

(C) The reactor was started up using the larger column described earlier. It was first packed with 220 cubic inches of untreated unglazed porcelain Berl saddles. Using the same feed rates and materials as before, the reactor ran 25 hours before polymerization in the packed section forced a shutdown. A total of 13,600 grams of crude isobutyl methacrylate had been collected, which is 61.8 grams of product per cubic inch of Berl saddles.

(D) The packing of the reactor used in above C was then replaced with the same amount of A1" unglazed porcelain Berl saddles treated as described in part B. Running at the same feed rates and with the same materials as before for 60 days, a total of 239,360 grams of crude isobutyl methacrylate was collected. This is equivalent to 1,090 grams of product per' cubic inch of Berl saddles. The reactor was shut down for modification. Examination of the packing did not disclose any polymer formation.

It will be noted from above Example 1A and C wherein untreated Berl saddles were employed, that the yield of product was only 57 and 62 g./cubic inch of packing, respectively, before polymerization became severe enough to force a complete shutdown of the reactor. However, when the acid treated Berl saddles were employed as in above Examples 1B and D, the yield of product increased to about 890 and 1090 g./ cubic inch of the treated packing, respectively, before the reactors were shut down for reasons other than polymerization. Thus, the final capacity of the packing treated according to the invention to prevent polymerization is not accurately known, but all the evidence points to an active life period much greater than 18 times that of the untreated packing.

Example 2 Clean unglazed porcelain Berl saddles were covered with a mixture prepared from equal volumes of fuming sulfuric acid percent sulfur trioxide) and concentrated nitric acid. After 12 hours the acid mixture was poured off and the saddles were Washed twice with water. The treated packing was used in a reactor employed in the preparation of isobutyl methacrylate by the reaction of isobutanol, water, strong sulfuric acid, and methacrylamide. Phenol and air were used during the process to inhibit polymerization in the reboiler section of the reactor. After ten days of continuous operation no polymer was formed in the packed section of the reactor but on replacing the treated Berl saddles with untreated Berl saddles and running the unit as before the packed section of the reactor became plugged with polymer after only 12 hours of operation. On replacing the untreated Berl saddles with Berl saddles treated as described, the reactor was operated for two months without any visible polymer formation in the packed section.

Example 3 Cleanunglazed porcelain Berl saddles were covered with a mixture prepared from equal volumes of concentrated sulfuric acid and concentrated nitric acid. After 8 hours the mixture was removed from the Berl saddles and the saddles were washed twice with water. The treated packing was used to prepare a distillation column for the punfication of methacrylate esters. The distillation column was operated for two months without any visible polymer formation. The column operated under identical conditions but with stainless steel or untreated Berl saddles quickly became inoperative due to polymer formation.

While the invention has 'been illustrated in the above examples with just the preparation of isobutyl methacrylate, it will be understood that the methacrylamide intermediate in the examples can be substituted by a like amount of acrylamide to give the corresponding isobutyl acrylate in generally similar good yields/cc. of the acid treated packing. Also, the isobutanol employed in the examples can be replaced with a like amount of any alcohol that is capable of entering into esterification reactions with acrylic and methacrylate acids. In this regard it is noted that the OH group is the functional group of these alcohols and its reactivity is not affected even by relatively large radicals such as naphthalene and the like. Therefore, it is obvious to those skilled in the art that a great and diverse group of alcohols generally known to esterify acrylic and methacrylic acids may be successfully employed in the present invention. Examples of useful straight or branched, saturated aliphatic alcohols are methyl, ethyl, propyl, butyl, isopropyl, sec. butyl, tert. butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl dodecyl, tetradecyl, hexadecyl, Z-methyl-l-butyl, B-methyl-l-butyl, 3-pentyl, Z-methyl-l-pentyl, 2-ethyl-l-butyl, 4-methyl-2- pentyl, 2-heptyl, Z-ethylhexyl, 2-octyl, 5-ethyl-2-nonyl, and 2-methyl-7-etl1yl-4-undecyl. Other exemplary alcohols are the aromatic or cycloaliphatic alcohols, for example, benzyl, phenylethyl, chlorophenyl, cyclohexyl, cyclobutyl, cyclopentyl and the like. Other useful alcohols are 2-methoxyethyl, Z-ethbxyethyl, 2butoxyethyl, tetrahydrofurfuryl, o-tolyl, and 2-nitro-2-methyl propyl methacrylate.

Thus, the invention has wide applicability for preparing the various esters of methacrylic and acrylic acids by by appropriate selection of the alcohol that is reacted with the mentioned amide in accordance with the following reaction scheme.

ROH OH2=O H02 Ri-CONHZ Acid CH=(]3-COOR Ammonium salt wherein R stands for the radical of any alcohol which can esterify acrylic or methacrylic acid, and R stands for hydrogen or a methyl radical. Also, as hereinbefore indicated, the invention is efficacious for indefinitely long periods of operational time without polymerization difficulties, whereas the older methods only partially prevent polymerization. Another advantage of the invention is that the continuous addition of inhibitor compounds is not required in the region specified by this invention, i.e. in the reactor column. Further, this invention can be applied to manufacturing processes that would destroy or otherwise inactivate many of the usual organic inhibitors. The invention also eliminates the need to practice special operational procedures to remove polymer formed during normal operation as is the case with processes using only the conventional inhibitors.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

What we claim is:

1. In the process for preparing methacrylate and acrylate esters by the reaction of the corresponding amide with an alcohol that can esterify acrylic and methacrylic acids, in the presence of an aqueous solution of a strong acid selected from the group consisting of concentrated H HCl, and H PO the step of carrying out the reaction in a react-or packed with a silicic ceramic material that has been previously treated at from about 15 to about 60 C. with a mixture of concentrated sulfuric acid and concentrated nitric acid, whereby polymer formation is prevented in said reactor.

2. The process comprising contacting in a reactor an aqueous solution of a strong acid selected from the group consisting of H 80 HCl and H PO and a compound selected from the group consisting of acrylamide and methacrylamide, with the vapor of an alcohol selected from the group consisting of straight and branched chain, saturated aliphatic alcohols of from 1-12 carbons, benzyl alcohol, phenylethyl alcohol, cyclohexanol, cyclopenta- 1101 and cyclobutanol, in the presence of a silicic, ceramic material that has been previously treated at from about 15 to about 60 C. with a mixture for-med by the combination of fuming sulfuric acid and an inorganic nitrogen containing compound that is capable of releasing N0 on contact with said last named acid, whereby polymer formation is prevented in said reactor.

3. In the process for preparing isobutyl methacrylate by the reaction of isobutanol, water, sulfuric acid and methacrylamide, the step which comprises carrying out the reaction in a reactor column packed with a silicic ceramic material which has been previously treated at from about 15 to about 60 C. with a mixture of fuming sulfuric acid and concentrated nitric acid, whereby polymer formation is prevented in said reactor.

4. The process according to claim 3 wherein the said mixture is composed of equal volumes of concentrated sulfuric acid and concentrated nitric acid.

5. The process according to claim 3 wherein the said reaction is carried out in a continuous manner.

6. The process according to claim 5 wherein the said :erarnic material is unglazed porcelain Berl saddles.

7. The process according to claim 5 wherein a phenolic :ompound selected from the group consisting of phenol 1nd cresol, and air are added to the reaction mixture as )olymerization inhibitors.

8. The process according to claim 5 wherein additional vater is added in the form of steam to the base of the -eactor column.

5/1933 Van Hasselt 252-186 4/1946 Funsten 252-45O in 2,416,756 3/1947 Jilk 260-486 2,526,310 10/1950 Wiley et a1. 260486 2,786,730 3/1957 Eck et a1. 260-486 2,890,101 6/1959 Borrel et a1. 260-486 2,967,157 1/1961 Robinson ct al 252450 2,980,730 4/1961 Dobson 260486 2,987,542 6/1961 Modiance 260486 3,014,065 12/1961 Chatelin 260-486 3,022,339 2/1962 Enk et a1. 260-486 LORRAINE A. WEINBERGER, Primary Examiner. DANIEL D. HORWITZ, Examiner.

ALBERT P. HALLUIN, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,332,984 July 25, 1967 Hugh J. Hagemeyer, Jr., et a1.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 33, for "packaged" read packed line 41, for "proces" read process column 6, line 4, strike out "by"; lines 8 to 12, for that portion of the formula reading H O ROH+CH =C ROH+CH =C-CONH 2 Z H 0 read 2 2':;;;?

R CONH 2 R l 2 acid 1 Signed and sealed this 5th day of November 1968.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN THE PROCESS FOR PREPARING METHACRYLATE AND ACRYLATE ESTERS BY THE REACTION OF THE CORRESPONDING AMIDE WITH AN ALCOHOL THAT CAN ESTERIFY ACRYLIC AND METHACRYLIC ACIDS, IN THE PRESENCE OF AN AQUEOUS SOLUTION OF A STRONG ACID SELECTED FROM THE GROUP CONSISTING OF CONCENTRATED H2SO4, HCL, AND H3PO4, THE STEP OF CARRYING OUT THE REACTION IN A REACTOR PACKED WITH A SILICIC CERAMIC MATERIAL THAT HAS BEEN PREVIOUSLY TREATED AT FROM ABOUT 15 TO ABOUT 160*C. WITH A MIXTURE OF CONCENTRATED SULFURIC ACID AND CONCENTRATED NITRIC ACID, WHEREY POLYMER FORMATION IS PREVENTED IN SAID REACTOR. 